Commit 145cc42f authored by Alexandru Elisei's avatar Alexandru Elisei Committed by Oliver Upton
Browse files

KVM: arm64: Copy FGT traps to unprotected pKVM VCPU on VCPU load 



Commit fb10ddf3 ("KVM: arm64: Compute per-vCPU FGTs at vcpu_load()")
introduced per-VCPU FGT traps. For an unprotected pKVM VCPU, the untrusted
host FGT configuration is copied in pkvm_vcpu_init_traps(), which is called
from __pkvm_init_vcpu(). __pkvm_init_vcpu() is called once per VCPU (when
the VCPU is first run) which means that the uninitialized, zero, values for
the FGT registers end up being used for the entire lifetime of the VCPU.
This causes both unwanted traps (for the inverse polarity trap bits) and
the guest being allowed to access registers it shouldn't.

Fix it by copying the FGT traps for unprotected pKVM VCPUs when the
untrusted host loads the VCPU.

Fixes: fb10ddf3 ("KVM: arm64: Compute per-vCPU FGTs at vcpu_load()")
Acked-by: default avatarWill Deacon <will@kernel.org>
Tested-by: default avatarFuad Tabba <tabba@google.com>
Reviewed-by: default avatarFuad Tabba <tabba@google.com>
Signed-off-by: default avatarAlexandru Elisei <alexandru.elisei@arm.com>
Reviewed-by: default avatarMarc Zyngier <maz@kernel.org>
Link: https://msgid.link/20251216103053.47224-2-alexandru.elisei@arm.com


Signed-off-by: default avatarOliver Upton <oupton@kernel.org>
parent 8d8e882c

arch/arm64/kvm/hyp/nvhe/hyp-main.c

+3 −0
Original line number Diff line number Diff line
@@ -180,6 +180,9 @@ static void handle___pkvm_vcpu_load(struct kvm_cpu_context *host_ctxt) 
		/* Propagate WFx trapping flags */

		hyp_vcpu->vcpu.arch.hcr_el2 &= ~(HCR_TWE | HCR_TWI);

		hyp_vcpu->vcpu.arch.hcr_el2 |= hcr_el2 & (HCR_TWE | HCR_TWI);

	} else {

		memcpy(&hyp_vcpu->vcpu.arch.fgt, hyp_vcpu->host_vcpu->arch.fgt,

		       sizeof(hyp_vcpu->vcpu.arch.fgt));

	}

}

arch/arm64/kvm/hyp/nvhe/pkvm.c

+0 −1
Original line number Diff line number Diff line
@@ -172,7 +172,6 @@ static int pkvm_vcpu_init_traps(struct pkvm_hyp_vcpu *hyp_vcpu) 


		/* Trust the host for non-protected vcpu features. */

		vcpu->arch.hcrx_el2 = host_vcpu->arch.hcrx_el2;

		memcpy(vcpu->arch.fgt, host_vcpu->arch.fgt, sizeof(vcpu->arch.fgt));

		return 0;

	}